The invention relates to a sonotrode for an ultrasonic surgical instrument having a shaft and an instrument head at the distal end of the shaft. The instrument head is equipped with a cutting structure for the treatment of bones. A helical cut-out is formed on the shaft. The invention moreover relates to a method for producing such a sonotrode.
By way of example, such sonotrodes can be used in dentistry to sever or ablate bone material of the patient. An ultrasound transducer creates a high-frequency mechanical vibration. The sonotrode is connected to the ultrasound transducer and is made to vibrate by the ultrasound transducer. When the cutting structure of the sonotrode is brought into contact with the bone, bone material is ablated by the high-frequency vibration.
It is known that a longitudinal vibration created by the ultrasound transducer can partly be converted into a torsional vibration of the instrument head by virtue of providing the shaft with helical cut-outs; in this respect see US2009/0236938A1, US2006/0041220A1, WO2010/049684A1. The shaft intrinsically twists as a result of the helical cut-outs when the longitudinal vibration from the ultrasound transducer acts on the proximal end of the shaft. As a result, the instrument head at the distal end of the shaft is excited to perform a torsional vibration.
In general, the amplitude of the torsional vibration increases the deeper and the wider the helical cut-outs cut into the material of the shaft. However, it is not possible to increase the amplitude of the torsional vibration arbitrarily in this fashion because the shaft must not be weakened too much by the cut-outs.